Dynamics and control of a 7-DOF hybrid manipulator for capturing a non-cooperative target in space

Abstract

This paper proposes a 7-DOF hybrid serial-parallel manipulator for capturing a non-cooperative target in space and discusses its dynamics and control. The hybrid manipulator is connected in a series by a 3-DOF parallel part with 1-PU&2-PUS configurations and a 4-DOF serial part with a 4R configuration. First, the UP-RRRR equivalent serial mechanism is presented for the kinematic analysis of the hybrid manipulator. Utilizing the Newton-Euler method, the dynamic model of the equivalent serial mechanism is derived in a recursive form. Then the dynamic equations of the parallel part in recursive form are also developed using the Newton-Euler method. Based on the complete dynamic model, we propose a control scheme for a hybrid robot to capture a non-cooperative target in a zero-gravity environment, including three modules: admittance control, motion estimation of the target satellite, and feedforward of the reaction forces. Finally, experimental results of full physical experiments based on air-bearing testbeds confirm the validity of the proposed control scheme for the hybrid robot to capture a non-cooperative target in space.